Nice e-book reader you’ve got there, Barnes & Noble. It would be a shame if something were to happen to it. And something just did.

Since its debut in April, Barnes & Noble Inc.’s
Nook Simple Touch with GlowLight
has been my favorite pure e-reader, thanks to a feature that illuminated the screen, so you could read in a darkened room. But the leading maker of e-readers, Amazon.com, was working on a similar device. The result, the new Kindle Paperwhite, is now number one. With a starting price of $119, it’s thinner and simpler than the Nook, with a superior lighting system.

Like the Nook, the Kindle Paperwhite uses black-and-white screen technology developed by E Ink Corp. of Cambridge to produce images that resemble ink on paper. Unlike laptop or tablet screens, the E Ink system doesn’t use a rear-mounted lamp to illuminate the screen. As a result, screen images are more paper-like than those viewed on a laptop or tablet, and far easier on the eyes. But until recently, viewing an E Ink screen required an external light.

Nook’s GlowLight system solved that problem with glowing diodes built into the upper edge of the screen. It works well enough, though the light looks somewhat uneven. Amazon claims to have spent four years working on its lighting system. If so, it was time well spent. Pages radiate an even glow, with only a hint of dimming along the lower edge. Amazon says font resolution is far sharper than in earlier Kindles. I didn’t see that much of a difference. But the screen made reading much more comfortable, even in a well-lighted room.

Amazon’s also doubled down on touchscreen technology, abandoning the menu button of its previous touchscreen device. There’s only an on-off-sleep button. To turn pages, just tap the screen — right edge forward, left edge backward. Tapping the top edge reveals the control menu. The touch response is snappy, and there’s less of that annoying effect where a page turns black before changing. On the Paperwhite, that only happens every fifth or sixth page turn.

The Nook Simple Touch has page-turn buttons on its edges, to supplement its touchscreen. The Paperwhite doesn’t, which might partly explain its sleeker shape. It’s just a couple of millimeters thinner than the Nook, but even that tiny difference made it more comfortable to carry.

The version I tested, priced at $179, includes Kindle’s superb Whispersync service, a 3G cellular modem that lets you download new books pretty much anywhere, with no wireless data charge. But most users can do their book buying at home or work, using the Wi-Fi Internet connection found in the base model.

Both the Nook and the Kindle Paperwhite provide access to hundreds of thousands of books, but only the Kindle has a feature called X-Ray that generates a sort of instant index. Press the X-Ray icon, and you get a listing of the key characters, locations, or events in book and the pages where they’re mentioned. It only works for a limited number of titles, but it’s a major benefit for serious readers.

Good as it is, the Paperwhite isn’t an automatic buy. Amazon’s own Kindle Keyboard 3G is a worthy alternative. No, the screen doesn’t glow, and it uses clumsy pushbuttons. But at $139, you get Whispersync 3G book downloads and a built-in audio system to listen to music as you read.

Besides, the Nook Simple Touch is still an excellent product, and its new price of $119 matches that of the Kindle. The Nook comes with a Micro SD
memory slot that will greatly expand its two gigabytes of memory; with the Paperwhite, two gigs is all you get.

The cheapest Paperwhite displays advertisements on its menu and sleep screens; the advertisement-free version costs $139. I don’t mind the ads myself, but the Nook is ad-free. And the Nook comes with an AC power adapter for recharging at a wall socket. It’s a $9.99 option on the Paperwhite.

If you’re still interested in buying a Nook, go right ahead. You won’t regret it. But now that the leading maker of e-readers has entered the glow-in-the-dark market with an excellent offering, the Nook’s long-term future seems a bit dimmer.